Research on the mechanisms of action of drugs that cause hallucinations in man has emphasized the idea of a relationship between the drugs and brain monamines. Behavioral models in animals of catecholamine activity have been important in the development of hypotheses about roles for dopamine and norepinephrine in the actions of the drugs. This project is concerned with models of serotonin receptor activation to the extent they can be used to probe for basic mechanisms for hallucinogens. The influence exerted by the drugs on serotonin mechanisms are being studied two ways: with a rat behavioral syndrome, and with a field potential evoked in vivo from the hippocampus of the anesthetized rat. Our immediate goals: complete experiments with beta-phenethylamine and its halogenated derivatives as inducers of the behavioral syndrome; continue experiments with changes in the field potential brought about by raphe nucleus stimulation, hallucinogenic agents (LSD especially), and serotonin antagonists (methysergide). The experiments will continue to test the unifying hypothesis that hallucinogens, regardless of chemical structure, all have in common the property of activating serotonin receptors, either directly or indirectly.